In a number of industries, particularly in electronics and electric power generating facilities, high purity water is necessary for effective process or manufacturing control. Particularly in the electronics industry, wherein both ionic and non-ionic impurities must be reduced to essentially zero, high purity water is essential. A number of systems have been developed to produce such water, the most prevalent being reverse osmosis procedures and ion exchange processes using successive two- or three-bed ion exchange systems. Such ion exchange beds rely upon anion and cation exchange beds for removal of impurities. A typical ion exchange resin bed is comprised of resin beads having a diameter of about 6-12 mm, with a random size distribution. Such ion exchange resin beds consist of a plastic backbone to which active or functional groups have been attached. The polymeric strands of the plastic backhone are connected through a network of cross-linking bonds that give each bead physical strength to withstand the hydraulic force generated during the demineralization cycle.
In strongly acidic and basic resins, the functional groups consist of an ionic pair. During service, the soluble contaminants enter the resin from the bulk water supply and exchange with the mobile ionic groups. The process reverses during regeneration, where contaminants are replaced by H.sup.+ or OH.sup.- groups in the case of strong-acid and -base resins, respectively.
Ion exchange systems have evolved into two and three bed systems employing a strongly acidic cation resin (H.sup.+) followed by a strongly basic anion resin (OH.sup.-). Typically, this two bed system is followed by a mixed bed having both cation and anion resins for polishing the effluent of the two bed train.
The net result of such systems is deionized water, a highly corrosive liquid which is an aggressive solvent. Deionized water is chemically unstable-it will re-ionize if contacted by ionic contaminants. Therefore, production and storage facilities must be configured to prevent contamination.
Because of the highly corrosive nature of the deionized water, as well as the strong acids and bases used to regenerate the cation and anion exchange beds, respectively (HCL or H.sub.2 SO.sub.4, and caustic sodium hydroxide), the materials utilized in the manufacture of process components (such as tanks and conduits) must be capable of withstanding extreme conditions. Stainless steel, or various steel alloys well known to those skilled in the art, are used for such purposes. Likewise, all fittings and weld seams must be equally corrosion resistant.
The vessels utilized in the production of deionized water utilizing ion exchange resin beds as set forth above, may be rated, for instance, at 250 gallons per minute throughput. Such vessels are pressurized, at a pressure of about 100 psi, to create and maintain flow therethrough. Generally speaking, the vessels are circular cross-section and are provided with rounded or curved vessel bottoms (the vessel "dome") to better withstand the internal pressures generated. Most such systems are provided with a "false bottom" within the vessel, a flat bottom across the vessel and above the bottom dome, to insure uniform movement of water through the resin bed retained by the false bottom, which would not be possible if the resin bed were asymmetrically retained by the domed bottom. In order to protect the metal components of the vessels, the interior portions exposed to the deionized water and resins are lined with an impervious lining, such as PVC or natural rubber.
The false bottoms in such vessels present a problem in water flow exiting the vessel: either the effluent water must flow into the dead space between the false bottom and the domed bottom to be drained therefrom or it must be transported therethrough with a conduit. In the first instance, the entire space between the false bottom and the domed bottom must be lined with a corrosion-resistant coating similar to that used to line the vessel. Because the coating must be applied after the false bottom is welded in place, access within the space between the false bottom and domed bottom is extremely limited, thereby making effective application of the lining in this area extremely difficult. In the second case, the conduit has been placed within a line sleeve which interconnects the interior of the vessel above the false bottom and the exit pipe from the bottom dome. In this second case, it is difficult if not impossible to effectively prevent water and/or resin from stagnating in the space between the sleeve and the throughpipe which conducts the water from the vessel. Such stagnant water area inevitably results in excess corrosion or organic contamination of the purified water.
The apparatus of the present invention eliminates the need to line the interior of the dead space between the false bottom and the bottom dome, and eliminates the stagnant space between the throughpipe and the sleeve. Therefore, the present invention provides a deionizing water vessel which is easier to construct and exhibits less corrosion and contamination than that possible through use of prior art apparatus'.